The present invention concerns a linear rolling bearing comprising a guide carriage that can be mounted through rolling elements on a guide rail. Linear rolling bearings of this type are used, for example, in the construction of machine tools in which a tool or a work-piece, for instance, is fixed on the guide carriage for moving along the guide rail.
One such linear rolling bearing is known, for example, from EP 0 846 880 A1. The guide carriage of this bearing comprises at least one endless channel for rolling elements. This rolling element channel comprises a load-bearing channel for load-bearing rolling elements, a return channel for returning rolling elements and, at both ends of the load-bearing channel and the return channel, a deflecting channel which connects these channels endlessly and deflects the rolling elements out of the return channel into the load-bearing channel and vice versa. The rolling elements are received in pockets of a cage strip having two free ends. As seen in circulating direction, the cage strip comprises spacers arranged between successive rolling elements, and cage belts arranged on both sides of the row of rolling elements connect the spacers to one another, the cage belts being received in guide channels of the rolling element channel for guiding the cage strip in the rolling element channel. The guide channel is formed by an open groove. During the operation of the linear rolling bearing, the ball chain circulates endlessly in the rolling element channel, the balls rolling on raceways formed on the rail and the guide carriage. The cage strip is deflected out of its longitudinally stretched position into a curved path when it leaves the load-bearing channel or the return channel and enters the deflecting channel. To prevent the free ends of the cage strip from tilting when they are deflected out of the longitudinal direction into the curved path, the cage belts are rounded off, so that an assumed center point axis of this rounding is perpendicular to the longitudinally stretched cage belt. The rounded-off cage belts end in a common spacer. The free ends of the cage strip consequently have a conical taper.
Over its operative life, the cage strip can get deformed as a result of mechanical loading, temperature influences, wear etc. This deformation can lead to an elongation of the cage strip. This means that the adjacent free ends of the cage strip can come into contact with each other. Especially when one of the two free ends of the cage has already entered the deflecting channel, while the other free end is still in the load-bearing or the return channel, these two adjacent free ends are in a slanting position to each other. In case of a contact between these two free ends, they can get hooked to each other because these tapered free ends describe together with the laterally entering cage strips, a canted contour that favors this hooking. Such a hooking of the free cage ends to each other can, however, lead to blocking and thus to failure and destruction of the linear rolling bearing.
It is an object of the invention to provide an improved linear rolling bearing of the pre-cited type in which the free ends of the cage strip are flawlessly guided and a contact between the adjacent free ends of the cage does not interfere with the perfect circulation of the cage strip.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that each of the two adjacent free ends of the cage strip has a movable leg that is arranged substantially crosswise to the cage strip, and opposing end surfaces of the legs are configured as contact surfaces for the legs with each other. When, as in the situation described above, one of the free cage ends has already entered the deflecting channel, while the adjacent free end of the cage strip is still in the load-bearing channel or in the return channel, the two legs of the two free ends can come into contact with each other. Due to the fact that the legs are arranged crosswise to the cage strip, they define a wedge-shaped gap between them in this situation. A contact between the two legs therefore takes place below the cage belts. Under this contact, the legs deflect i.e., they right themselves to each other. The point of contact between the legs thus shifts toward the cage belt, so that a pressure force between the abutting contact surfaces, as far as it is effective, is transmitted at the level of the cage belts. In other words, any occurring pressure force is transmitted into the neutral fiber of the cage strip, so that no undesired forces are introduced crosswise to the cage belt. The contact surfaces are preferably made smooth and flat. But they may also be smooth and have a slightly curved contour, in which case, an assumed center point axis of this curved contour is arranged crosswise to the direction of circulation of the rolling elements and perpendicular to a plane in which the rolling elements circulate. The flawless circulation of the cage strip can also be supported by rounding off the ends of the cage belts, with an assumed center point axis of this rounding being arranged crosswise to the direction of circulation of the rolling elements and perpendicular to a plane in which the rolling elements circulate. Such roundings on spacers are known, per se, for example, from JP 63-123824 U1.
The legs are preferably arranged within a cross-sectional opening defined by the rolling element channel and outside of the aforesaid guide channels. If rollers are used as rolling elements, it is particularly advantageous if the leg substantially fills the cross-sectional opening of the rolling element channel. This means that, as seen in circulating direction of the rolling elements, the leg describes a substantially rectangular or square contour. In any case, the leg spans within the rolling element channel a sufficiently large surface that is dimensioned so that a hooking of the adjacent legs into each other and a deflection of the legs is not possible. If the leg is unsupported, the required mobility can be achieved by making the leg with thin walls out of a flexible plastic, so that the free ends of the leg can be deflected without the need of noteworthy forces. The leg preferably has a plate-like configuration, the front end surface of the leg oriented away from the free end of the cage strip being flat. If adjacent, plate-like legs come into contact with each other, a sliding movement takes place between the abutting contact surfaces of the legs which excludes the possibility of tilting or hooking.
The leg is preferably formed integrally on the spacer and/or on the cage belts at the level of the cage belt and extends from there in the direction of a space axis arranged perpendicular to the underside of the cage belt. Because, as mentioned above, the legs are movable and right themselves to each other, the transmission of any pressure force occurring between the contact surfaces takes place only at the level of the belt i.e., in the neutral fiber, without any forces acting crosswise to the direction of circulation on the cage strip. A perfect guidance of the cage strip is thus guaranteed.
It may be of advantage in certain uses if the leg additionally extends in the direction of a space axis arranged perpendicular to the upper side of the cage belt i.e., if it has a T-shaped configuration. This feature of the invention offers the advantage that the cage strip can be inserted into the linear rolling bearing without attention having to be paid to the underside or the upper side of the cage strip.
The mobility of the leg proposed by the invention can also be achieved with the help of an articulation connecting the leg to the spacer and/or the two cage belts. In this case, the leg itself can be made of a rigid material. This articulation can be made, for example, as a film joint which can be provided already in the injection molding die so that it is of a technically simple nature and economically interesting. Similar to a film joint, it is also possible to use an elastically deflectable web that is connected on one side to the leg and on the other side to the spacer and/or the two cage belts. This embodiment of the invention is likewise particularly suitable for the fabrication of the cage strip by injection molding.
The leg and the articulation can be made in one piece with the spacer or the two cage belts. This embodiment, too, is particularly suitable for an injection molding method in which the cage strip is made of plastic.
In place of an articulation, the leg itself can have a flexible configuration. This is possible if the leg is made with thin walls out of a flexible plastic.
The part to which the leg is connected can be a spacer but may also have another configuration.
To assure that any pressure force occurring between the two abutting cage ends is transmitted at the level of the cage belt, the leg may comprise a projection forming a part of the contact surface at the level of the cage belt. When the free ends of the cage strip contact each other below the cage belt and then right themselves to each other, further contact takes place at these projecting portions so that it is assured that the transmission of pressure force is effected at the level of the cage belt.
The invention will now be described more closely with reference to four examples of embodiment illustrated in a total of nine appended figures.